Electrical musical instrument



Aug. 3l, 1943. w. E. KOCK ELECTRICAL MUSICAL INSTRUMENT Filed April 23, 1941 2 Sheets-Sheet l zow/ESQ N wIPO 20mm Q U U K w RD N 0 R MN o.

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ELECTRICAL MUSICAL INSTRUMENT Filed April 23, 1941 2 sheets-sheet 2v FR OM OSCILLATORS 1L 1 INVENTOR WlNsToN E.KocK

ATTORNEY ducing means.

Patented 31, 1943 UNITED STATES v:raciti-:rrr ori-ical 2,328,282 ELECTRICAL MUSICAL INSTRUMENT Winston E. Kock, cincinnati, olii, assigner u The Baldwin Company, Cincinnati, Ohio' Application April z3, 1941 ,seriai No. 389,939

i a claims. (ci. s41.o1)

My invention relates to the electrical production of music. More particularly it relates tothe type of production in which complex electric oscillations representing musical scale frequencies g -such sufiicient harmonic content that various tone colors may be secured without the necessity of adding oscillations together.

A primary object of the invention is to provide I an oscillation generating and keyboard switching system in an electrical musical instrument such that one oscillator may be employed for sev- I eral adjacent notes. In accomplishing this, whereby a lesser number of oscillators is contained than there are notes in an instrument, a considerable economy is effected and a low cost musical instrument may vbe provided. In this regard I have considered the number of notes to be associated with an oscillator, and it is therefore an object to relate the number of notes and oscillators such that most music can be adequate-A ly played on the instrument.

Another object of the invention is to provide an electrical musical instrument in which music played on a keyboard in one tone color may be accompanied on the same keyboard in another tone color.

In keeping with the above objects is an object to 4provide both pedal and manual keyboards in an instrument.

It is also an object to provide a keyboard. switch organization such that electrical transients occurring on the operation of the key switches (sometimes called key clicks) are avoided.

The manner in which the above objects are attained and the attainment of those objects which will be pointed out hereinafter or occur to those skilled in the art on reading this specification, will now be described in detail, reference being made to the accompanying drawings wherein:

Figure l is a wiring diagram of a musical instrument constructed according to the invention, illustrating an oscillation generating system, a tremolo oscillator, a keyboard switching system, tone color circuits and the inter-connections betweenl these parts, the figure also indicating connections to other keyboards; Figure 2 is a wiring diagram of a frequency divider and keyboard switching system, particularly adapted for pedal keyboard use when employed in conjunction with a primary oscillation generating system; and

VFigure 3 is a wiring diagram of an oscillation lgenerating and key switching system; also adapted particularly for pedal keyboard use.

With specific reference to Figure 1 I have shown a series of electrical audio frequency oscillators each comprising a vacuum tube T having an anode A, a thermionic cathode K and a grid G interposed between these elements. In principle the oscillatory circuits associated with each tube are of conventional character. Thus the grid-to-cathode circuit includes an oscillatory couple comprising a parallel arrangement of an inductance In and capacity C. Interposed between this oouple and the grid is a parallel combination of a resistance R1 and a condenser Cs,

the purpose of which is to maintain proper negative bias on the grid during operation.

The anode-to-cathode circuit comprises in order a coil L2 regeneratively coupled to the grid circuit coil L1 through a. common ferromagnetic core as shown, a resistance R2 and a source of positive plate potential +B. This source of "direct current voltage, as well as any others which may be employed in the instrument, may of course be derived by rectiiication and filtering from commercial alternating current supply and ground may of course be employed for the other terminals of the sources. In factI employ ground throughout as a return for all circuits, indicating it by the conventional symbol wherever necessary in the drawings, as particularly pointed out at g in Figure 1.

The couple LiC of the grid circuit is tuned to an audio frequency corresponding to a note in the musical scale (or selective notes as will be further pointed out) and as above indicated the anode circuit is regeneratively coupled thereto through the coupled coil L2. As illustrated the two coils L1, L2 preferably are mounted on a common ferromagnetic core.

The oscillator thus operates in a usual way as will be recognized by those skilled in the art, generating electric oscillations for a particular note. 'I'he oscillations within the tuned couple LiC are substantially sinusoidal, but I have found that by giving proper values to the parallel elements R1 and Cs the oscillations in the anode circuit, from which I derive oscillations for tone production, are sufficiently complex, i. e., have sufficient harmonic content for the purpose set forth early in this description.

It will be noted that the grid circuits of all audio frequency oscillators of Figure 1 are connected to a bus i which is in turn connected to the tuned circuit of an oscillator havinga tube T. This latter oscillator is similar in construction to the tone producing oscillators but is arranged to operate at a sub-audio frequency of say 6 C. P. S. (cycles per second). I have found that oscillators such as indicated in Figure 1 have adequate stability for tone productive purposes but that their frequencies can be varied slightly by application of sufficient voltage to their grids. This voltage I supply as alternating voltage from the oscillator containing the tube T', at a sub-audio rate and in this way a pleasing pitch tremolo or vibrato may be given to the musical tones produced by the instrument. A switch Si (preferably appearing as a tab at the console of the instrument) located in the anode circuit of the sub-audio oscillator is used to turn the tremolo on or off as desired.

I have indicated generally above that any one audio oscillator is used for several notes selectively- Taking this up specifically the capacity C of each of the audio oscillators of Figure 1 comprises a number of condensers connected in parallel through a key switching arrangement. As illustrated these condensers comprise a fixed condenser C1 permanently connected across the coil Li, an adjustable condenser C2 permanently connected to Ci, an adjustable condenser C3 connected to C2 through a key operated switch S2, and an adjustable condenser C4 connected to C3 through a key switch S3. To point out that the switches are key operated, a playing key M and pull rod is shown associated with a switch S2, it being understood that playing keys are also associated with the other switches respectively, these keys being arranged to a manual keyboard.

Also associated with each playing key is a gradual contact switch S4, of a type which closes gradually, iirst through a high resistance and thence through a progressively decreasing resistance. The type of switch set forth in United States Patent No. 2,215,124, entitled Electrical contact, issued September 17, 1940, to John F.

Jordan andvmyself as joint patentees, is satisfacr tory in this instance.

Thus it will loe noted that three playing keys and their associated switches are indicated for each audio frequency oscillator in Figure 1. It will also be specifically noted for each oscillator that the switches associated with one playing key comprise a gang arrangement of a condenser switch S2 and a gradual contact switch S4, the switches associated with a second playing key comprise a gang arrangement of the condenser switch S3 and a gradual contact switch, while the third key operates only on a gradual contact switch.

As aforeindicated I derive oscillations for tone production from the anode circuit of each oscillator. As specifically shown the tone output arrangement comprises a series combination of a condenser Ct (for isolating-i-B from the output) and a resistance R3 connected between the tube anode end of the resistance R2 and ground. The tone output lead 2 is connected to an intermediate point of the resistance R3 and connected to this lead are the movable arms 3 of the gradual contact switches S4. The vstationary resistances R4 of these switches, over which the switch arms roll, are connected to a further lead 4 which in turn is attached to an oscillation collector or header 5 (or 6) The characteristics of this header have been fully described in my United States Patent No. 2,233,948, issued March and the frequency cf each oscillator is that corresponding to all of its condensers Ci, C2, CJ, and C4 being engaged in its tuned couple LiC. Taking for example the oscillator at the top of Figure 1 its frequency under this condition may be 116.5 C. P. S. (a low A# in the equitempered scale based upon A=440). Depression of the key connected only to a switch S4 (at the right) therefore directs the oscillator output at this frequency into the header 5. Depression of the key connected to the switch S3 and a switch S4 however, opens switch S3 thereby removing the condenser C4 from the tuned couple and raising the oscillator to a higher frequency which may be that of the adjacent note B=123.5 C. P. S. It also closes the corresponding switch S4 and thereby directs the oscillator output at this latter frequency into the header 5. Similarly, depression of the key connected to the switch Sz and a switch S4 removes the condensers C3 and C4 from the tuned couple thereby further raising the oscillator frequency to the adjacent note :130.8 C. P. S. and directing the oscillator output at this frequency into the header.

In this way each oscillator provides three notes selectively. Thus in a sixty-one note keyboard for example, only twenty oscillators are required (the four lowest notes may be connected to one oscillator) and by employing double tubes, i. e., tubes in which elements for two tubes are enclosed in a single envelope, only ten apparent tubes are required for an oscillator system.

I have mentioned above that the condensers C2, Ca, and C4 of each oscillator are adjustable. This of course is to provide for tuning of the oscillator to its respective frequencies, the adjustable condensers being small in comparison with the condenser Ci which provides most of the capacity necessary.

It is of course not possible to play certain note combinations in a system such as the foregoing. I have found however that by the choice of the number of notes indicated in the above for each y oscillator, most music can be played on the instrument. This is particularly true in regard to music of lesser complexity, such as popular music (soecalled), folk music, patriotic music, church hymns, etc. When this and the economical construction and small space requirements of the instrument are considered I believe the arrangement will provide an acceptable unit in the field of music.

Sequence of operation of the switches in gang switch combination such as S2S4 and S354 is important and I provide a switch operation such that as a key is depressed the condenser switch, Sz for example, opens before the corresponding gradual contact switch S4 operates. In this way the beginning and cessation of tones is prompt, but devoid of the unpleasant sounds known as key clicks or key thumps, caused by electrical transients. As aforementioned the switch construction set forth in the Patent No. 2,215,124 is adequate for the gradual contact switches in this case.

the Viola has a resistance Re and condenser Cio' in series, shunted at their junction point by a It will also be noted in Figure 1 that the oscillator outputs have connections to other keyboards (as so marked). The same oscillators in this regard may be employed for more than one keyboard, whether manual or pedal, and I shall discuss in detail later the application of a pedal keyboard. As to a manual keyboard I prefer to divide the oscillators into two groups. In a sixty-one note keyboard' for example, ranging from C=65.4 C. P. S. to C=2093 C. P. S., I prefer to divide the oscillators at the point between the notes C (middle C) :261.6 C. P. S. and C#=277v.2 C. P. S., directing the oscillations of the bass group of oscillators into one oscillation collector or header and the treble group into another. This I have indicated in Figure 1 wherein the oscillator at the top of the iigure, which oscillator may be considered as a member of the bass group, is connected to the header `5, whereas'the oscillator at the bottom of the figure, of the treble group, is connected to another or treble header 6. To indicate that other oscillators of the bass and treble groups are connected to the headers respectively, additional leads 4 are illustrated partially in the gure.

Between the headers and the amplifier-loudspeaker system of the instrument I connect a plurality of oscillation modifying or tone color paths, as illustrated in Figure 1, selectable individually or in combinations as desired, the purpose of which is to alter according to various musical voices or timbresthe oscillatio-ns appearing in the headers according to the notes of musical compositions. An instrument of the same general type has been set forth in the aforementioned Patent No. 2,233,948, and as lin the patent the oscillations provided by the oscillators here have such suiiicient complexity that it is not necessary later to increase their complexity by non-linear devices or the like. Hence the tone color paths may be of linear character, comprising various combinations of inductance, capacity and resistance.

It will be noted in Figure l that one f the tonel color paths, marked Viola, is connected solely to the treble header B through a switch S5 (which preferably appears as a stop tab on the instrument console), another path, marked Bassoon, is connected solely to the bass header 5 through a similar switch S5, a third path marked Flute is connected to both headers and has a switch S5 in its output lead, whereas a fourth path marked Cello or Diapason is connected to the headers jointly or selectively through respective switches S5.

In this way many arrangements of voices are possible. A melody played in one voice on one part of a keyboard may be accompanied on another part of the same keyboard in another voice. In a modification of this a melody may be played in two voices and accompanied on the same keyboard in a third voice, or vice versa. One or more voices are of course available throughout the keyboard, and in view of the foregoing a considerable ilexibility in tonal eiects is provided.

Specifically the various tone color paths illustrated are comprised as follows: the Bassoon comprises a series resistance R5 and a parallel combination of inductance La and a condenser Cv, shunted to ground; the Flute contains the reslstances Re in series shunted at their junction points by the condensers Ca to ground, the connection from the treble header being to the second junction point (from the left); the Cello or Diapason has a parallel combination shunted to ground of a resistance R7 and a capacity Cs; and

resistance R9 to ground.

Each of the tone color switches S5 is of a stepped character closing iirst through a high resistance Rio and thence short circuiting this resistance. I iind that these switches sufliciently attenuate the clicks (similar to key clicks as mentioned above) ordinarily occurring on opening or Y be incorporated in the output system.

A particular means for providing a pedal keyboard organization in the instrument is illustrated in Figure 2. In have mentioned in the above that the 'manual keyboard associated with the oscillators and key switches of Figure 1 may have a pitch range from C=65.4 C. P. S. to C: 2093 C. P.4 S. This in the terminology of organists corresponds to a standard organ keyboard of eight foot pitch. To provide a pedal keyboard for the instrument at this same pitch I mechanically couple pedal keys to the condenserswitches S2, Sa. To indicate this I'have shown pull rods 8 attached to these switches in Figure 1, the rods being continued into Figure 2 wherein one of them is attached to a pedal operated key P. It will be understood that there are a plurality of keys such as P arranged at a usual pedal keyboard, mechanically coupled respectively, through the respective rods 8, to the switches Si, S2. Also associated with each key P is a gradual contact switch Si. Theser switches S4 have connections from the oscillators of Figure 1 (as so indicated) similar to the manner in which the gradual contact switches of Figure 1 are connected, and similarly the outputs of the switches have connections to an oscillation collector or header, indicated at 9. The dashed line in Figure 2 indicates the inclusion of a larger number of parts than th'ose specifically shown,

In this way by providing a pedal keyboard of thirty two keys (a usual number) associated with the thirty two lowest pitchnotes of Figure 1, an eight foot pitch pedal keyboard is provided, its keys operating to select appropriate frequencies from the oscillators of Figure 1 and to connect the oscillator outputs to the header 9. Through a lead Irthe output of the header 9 may in turn be connected to the output system of the instrument, through appropriate tone color paths interposed as desired.

It is also desirable to provide notes at the pedal keyboard an octave lower respectively than those indicated above, i. e., to provide oscillations at sixteen foot pitch in the terminology of organlsts. To do this I connect a frequency dividing device I I tolthe pedal header I0 and connect the output lead I2 of the divider to the output system of the instrument, again interposing'appropriatetone color paths as desired. The result of the action of the device II is to reverse the phase of alternate pulses of oscillations conducted to it from the header 9 upon depression of a pedal key P. Consequently the oscillations appearing in its output, lead I2 are an octave lower than those in the header 9, i. e., at the sixteen foot pitch aforementioned.

Taking up the device I I specifically there is shown a symmetrical arrangement including a double vacuum tube T" comprising a single envelope containing a common thermionic cathode K, two anodes A, and grids G interposed between the respective anodes and the cathode (I may of course substitute two single tubes for this double tube, connecting their cathodes together). The particular electrode circuits associated with the tube comprise a grid-to-cathode circuit for each half of the tube, including in series a small coil L4, a resistance R11, and a source of grid bias potential-l-C-common to the two grid-to-cathode circuits with its positive terminal connected to the cathode; andan anode-to-cathode circuit for each tube half, including in series a small coil L5 regeneratively coupled to the coil L4 of the corresponding grid-to-cathode circuit, a resistance R12, one half of the primary Le of a transformer LcL-r, and a source of positive plate potential-H3- common to the two anode-to-cathode circuits and connected to the center Vtap of the primary Le. The secondary L1 of the 'transformer LeLv, which has a ferromagnetic core as shown, is located in the output circuit l2 of the divider.

Bridging the respective junction points of the resistances Riz and coils La are two capacities Cn, C11 in series, and connected from the junction point of these two capacitiesto the center tap of the transformer primary Le is another capacity C12 of a much smaller relative value. As further illustrated there is a connection from the header 9 to the junction point of the resistance R11 and coil L4 of each grid-to-cathode circuit or the device il, a capacity C13 being placed in each of these connections.

In principle each half of the divider Il comprises an oscillator in which high frequency oscillations (which may be in the radio range) are generated owing to the regenerative action between its grir -to-cathode and anode-to-cathode circuits. (The coils I and L5 are regeneratively coupled as aforesaid and actuallycomprise each a couple consisting of the inductance of the coil y and its distributed capacity). "I'he bias potential-l-C is given such a value that the oscillators will not operate until excited into operation by` (The condenser C12 furnishes highfrequency conductance in the arrangement.) If theoretically both halves of the divider were exactly similar the action of the aforesaid first pulse would be to excite both halves into high frequency oscillation. In practice however such exact equality cannotv be obtained owing to differences in characteristics between the two halves of commercially made tubes such as T, and/or slight differences in the associated impedances, or can be deliberately avoided if necessary. 'I'he consequence of this is that one half of the divider leads" the other half. Let us suppose that the leading half is the left half in Figure 2. The effect of this is to block operation of the right half of the divider, the condensers C11 charging in a direction corresponding to increased anodeto-cathode current in the/left half.

Between the first and second pulses from the header 8 the left hall' of the divider attains a saturated, i. e., steady oscillatory conditionv so that the second pulse from the header has no further excitation effect upon it. This second pulse however excites the right half of the divider charging the condensers C11 in an opposite direction and blocking operation of the left half. The left side then operates on the third pulse, the right on the fourth, and so on. The result of this action is to produce in the secondary I n and output lead I2, a series of pulses of symmetrical waveform at half the frequency of the pulses in the header 9, i. e., at the aforesaid sixteen foot pitch.

Another means for providing a pedal keyboard organization is shown in Figure 3. In this figure a. separate oscillator generally similar to those of Figure 1 is illustrated, with a difference that the oscillator is adapted to operate selectively at a much larger number of frequencies. This number of selective frequencies may be thirty two, corresponding to the thirty two notes of eight foot pitch required in a usual pedal keyboard. I have denoted this in Figure 3 by the dashed lines, to indicate inclusion of a larger number of parts than those specifically shown. The adjustablecondenser Cn in this regard may indicate the thirty second member of a series. I have also shown a pedal operated key P, it being understood that there is a pedal keyboard of these keys, and as in Figure 1 condenser switches Si S2, etc., and gradual contact switches S4 are operated in gangs by the respective keys. To provide oscillations at sixteenfoot in conjunction with the oscillator of Figure 3, I have connected to its output header 9 the condensers Cu, Ci: to denote the connection to the oscillator of a frequency divider such as that of Figure 2 described above.

The following values are suitable in an exemplary combination of parts for apparatus such as the foregoing, in which tubes such as type 6SC7 double triodes may be employed:

Ri:l,000,000 ohms R2: 120,000 ohms Ra: 100,000 ohms (25,000 ohms between the lead 2 and ground) R5: v 50,000 Ohms Re: 50,000 Ohms R7: 50,000 Ohms Re: 100,000 Ohms Ra:1,000,000 ohms R1o=1,000,000 Ohms Cs :0.01 microfarads C9 :0.002 microfarads 010:5 0 micromicrofarads Cii:0.006 microfarads Ciz:0.002 microfarads Ci3:0.002 microfarads It will be understood that modifications may be made in my invention without departing from its spirit. Being thus described those features t contiguous frequencies in the musical scale, said oscillators having oscillation control means whereby they may be caused to oscillate selectively at said plurality of different frequencies.

and the keys of each group being connected to the oscillator of that group through the oscillation control means of said oscillator to control the frequency of the oscillations produced thereby to the notes represented by the said keys.

2. The structure claimed in claim 1 in which the keys of each group are so connected to the oscillator for that group that the simultaneous striking of a plurality of keys in one group will cause said oscillator to oscillate at but one frequency, namely the highest frequency represented by any key struck in said group 3. The structure claimed in claim 1 in which each group of contiguous keys consists of three keys.

4. The structure claimed in claim 1 in which each group of contiguous keys consists of three keys, and in which the frequency of each oscillator is controlled by'a plurality of capacities connected in parallel, two ofthe keys in each group being connected to break the circuit to certain of said capacities.

5. In an electrical musical instrument, a keyboard lhaving keys, a plurality of independent primary electric oscillation generators of lesser number than the keys of said keyboard, each of said oscillation'generators being associated with a separate group of three contiguous keys of said keyboard, said generators being capable of producing complex oscillations at selective frequencies corresponding to the keys of its group, an output system, a plurality of tone color paths connected to said output system, means for causing the keys to eifect the feeding of oscillations from said generators through said tone color paths to said output system, and means for selectively and simultaneously feeding oscillations from the several generators t0 said output system through different ones of said tone color paths.

I 6. The structure claimed in claim 1 including an output system, means for causing said keys to feed oscillations from said generators to said output system, and means intermediate said feeding means and said output system and effective over the entire range of the oscillations so fed for dividing the frequency of said oscillations.

7. The structure claimed in claim 1 in which each oscillation generator has connected with it a plurality of-capacities in parallel for determining the frequency of its oscillations, means for collecting oscillationsfrom said generators, said keys having switches for controlling the number of capacities eifective in said parallel capacity system, and switches for connecting said oscillation generators to said collecting means, said switches arranged to act sequentially in the order named, upon the actuation of a key.

8. In combination with oscillation producing means in an electrical musical instrument, producing a range of oscillation frequencies suitable for the rendition of music, a frequency divider comprising thermionic means providing two paths in which oscillations may be generated upon external excitation, and means for alternately rendering said paths ineffective, whereby external periodic excitation from said oscillation producing means will result in the production of oscillations derived from s'aid paths of a frequency which is a sub-octave of the excitation frequency, overthe entire frequency range of said oscillation producing means.

WINSTON E. KOCK. 

